Shift workers may be able to stay alert using a drug designed to treat the sleep condition narcolepsy, where people fall asleep involuntarily.

The company which makes Provigil has announced results from a test of the drug on over 200 shift workers which showed it can help "shift work sleep disorder"- excessive sleepiness caused by odd working hours.

But there are fears that Provigil (modafinil) could be used by healthy people just so they can work or play harder.

It is feared they could fail to get enough sleep, with potential ill effects on their health.

You stay awake, you're tired the next day, so you take something to keep you awake

Neil Stanley, British Sleep Society

Other studies have shown the drug helps helicopter pilots stay alert and capable of performing complex tasks for almost two days without sleep.

Provigil also appears to help patients with multiple sclerosis cope with fatigue.

More research is being done to see if it can also help tired truck drivers, medical staff and soldiers.

Cephalon, of West Chester, Pennsylvania, US, makes Provigil, which could soon be licensed for use for patients with other sleep disorders which cause daytime drowsiness, such as sleep apnoea, both in the US and the UK.

It will be making an application to the US Food and Drug Administration (FDA) this year.

Sleep experts say an application for a UK licence could be made in a couple of years.

Sleep deprivation

Some US doctors say patients with demanding careers and lifestyles are already coming to them asking for Provigil.

Provigil is thought to work by acting on the pre-frontal cortex in the brain, which is one of the most active areas of the brain in people when they are awake, involved in planning, memory and attention.

It means that people who have narcolepsy have an alternative to taking amphetamines to treat their condition.

Tests have shown that there was no noticeable need for a longer than usual sleep after someone had taken the drug.

But there are fears people may decide they can do without sleep, running the risk of cognitive impairment, and problems with the immune and hormone systems from sleep derivation.

Paul Blake of Cephalon admitted: "The drug isn't a replacement for sleep."

'Take sleep seriously'

Neil Stanley, chairman of the British Sleep Society, told BBC News Online: "If people take it during the week to keep them going during shift work, will they try to take it for Saturday night to help them go clubbing."

He said it could become as available as other products such as Proplus.

But he warned: "Taking it in a social situation would indicate that people do not take sleep seriously

"It's a Catch 22 situation. You stay awake, you're tired the next day, so you take something to keep you awake."